Data storage tape drives are widely used in data processing systems as either the primary data storage device or, more often, as a back-up data storage device to the system's hard disk drive. Conventional tape drives are designed to transfer data to and from a length of magnetically encoded tape, typically one-quarter inch in width, which is transferred between a supply reel and a take-up reel. While several tape drive designs exist for recording and playing back a data tape, the two most widely used drive technologies up to now have been stationary head tape drives for longitudinal recording and rotary head tape drives for transverse linear or "helical" recording.
In longitudinal recording, a tape drive includes a plurality of adjacent stationary heads which lie across the width of a data tape. In helical recording, one or more heads are provided around the circumferential surface of a rotating cylindrical drum. An advancing data tape encounters the rotating drum such that the longitudinal direction of the tape is angled with respect to the plane in which a recording head on the drum rotates. As such, rotary head helical recording provides a relatively large areal density.
Presently in the tape drive industry, as in other data storage technology areas, there is a movement toward decreasing drive dimensions while at the same time increasing data storage capacity. Existing longitudinal and helical recording technologies have proven inadequate in meeting these demands.
An alternative to the longitudinal and helical recording scheme is a recording scheme which incorporates an "arcuate scan" of the tape. In arcuate scan drives, a rotating drum having a plurality of heads mounted thereon is positioned perpendicular to the tape and rotated such that each head makes an arcuate path over the tape as the tape passes around the head drum. Arcuate scan recording has been known for some time, but has been disfavored due to the lack of effective servoing schemes for accurately maintaining alignment of the heads with the arcuate data tracks.
U.S. patent application Ser. No. 07/898,926, filed Jun. 12, 1992, by J. Lemke (hereafter "the Lemke application"), discloses a relatively compact arcuate scan tape drive for recording and playing back up to approximately 10 gigabits on a conventional mini-cassette tape, a storage capacity which is higher than that previously obtained with either longitudinal or helical recording. FIGS. 1-2 of the present application are reproductions of FIGS. 1-2 of the Lemke application and constitute a perspective view of the arcuate scan drive, and a top view of the head drum/tape interface. The Lemke application discloses a tape drive including a plurality of heads placed on the front circular face of a rotating drum, with the axis of rotation of the rotating drum being perpendicular to and intersecting with the longitudinal axis of the advancing tape. Head drum 30 rotates about axis 38 to pass heads 35 in arcuate paths, shown in FIG. 3, along tape 21 as tape 21 passes head drum 30. As the tape advances from the right to the left and the drum rotates in a counterclockwise direction, the heads trace arcuately-shaped data tracks 40, substantially transverse to the longitudinal axis of tape 21. As also shown in FIG. 3, arcuate tracks 40 are not entirely semicircular, as the motion of the tape causes a pitch change in the arcuate path as the head transverses the tape from bottom to top as shown in FIG. 3.
The Lemke application discusses a drum having a plurality of heads which utilizes a sequential, three head data transfer and positioning scheme. In the Lemke arrangement, the heads are arranged in triads where the first head is a read head, the second a write head and the third a servo head, each passing over a given track in succession. It should be readily understood that numerous head schemes are suitable for use with arcuate scan disk drives.
A significant concern in an arcuate scan drive, and indeed any information recording system wherein a rotating head drum section must electrically communicate with a stationary data channel and controller, is the commutation of the data signals from the stationary section to the rotating section. Generally, this involves use of a rotary transformer or a slip ring. In either alternative, there are limitations in the amount of signal which is successfully commutated from the stationary section to the rotating section. In the Lemke application, the rotating section is essentially passive, meaning that the data transmitted from the stationary section of the recording arrangement must be of sufficient strength to be passed by the heads to the tape.
Data storage devices generally include encoding means to code the "raw" data signal prior to recording onto the magnetic storage medium. Generally, raw data signals are unsuitable for recording by the recording channel as there is no bound on the D.C. component in the data stream. In a rotating transformer, when such signals are transmitted across the transformer, over time, the transformer voltage will tend to equalize to the area of greatest voltage, either more positive or negative.
When transmitting encoded data across a rotating transformer and providing such signals directly to a recording head, the encoding scheme must ensure that the coded data is free of any DC component or is "DC-free code." When such DC-free codes are utilized to encode data which must pass from the primary to the secondary of a rotating transformer, the inefficiency inherent in such codes reduces the overall storage capacity of the device.
An alternative to commutatively coupling data signals across a rotary transformer to recording heads is shown in U.S. Pat. No. 5,191,489. As shown therein, data and control information is transmitted via a rotary transformer and "transmission system," respectively, to the pre-amplifier on the rotating side of a helical scan recording arrangement. The pre-amplifiers then drive the recording heads directly while both are rotating adjacent to the storage medium. The system disclosed shows data signals transmitted over a four channel rotary transformer; four separate sets of data are transmitted to four amplifiers driving four recording heads. A "transmission system", separate from the rotary transformer and described with respect to the prior art as a slip ring, transmits control signals to the four amplifiers located on the rotating portion of the system. An encoder on the stationary portion of the read/write assembly encodes gain control signal data, a clock signal, and a digital-to-analog enable signal into a single synchronous stream of control for transmission across the "transmission system." A decoder on the rotating section separates the control data and provides the decoded control information to a digital-to-analog converter which controls the pre-amplifiers.
While this scheme is advantageous in reducing the size of the "transmission system" needed to transmit the pre-amp control data, two separate elements--a transmission system and separate four-channel rotary transformer--are required to transmit the data signals to the rotating section for information recording onto the data storage medium.
An alternative configuration for controlling pre-amplifier circuitry on a rotating section of a recording apparatus is shown in U.S. Pat. No. 4,851,935, wherein video data signals are transmitted to a rotating head in a scheme utilizing three rotary transformers. One of the transformers carries the data to be recorded, another carries switching information, and the third carries power to a separate erase head utilized during the write mode only. Switching between the multiple heads disclosed therein in various embodiments is accomplished through a Hall effect element or magnetic spindle which generates an alternating signal to a phase inverter which switches the data to be recorded between the heads solely based on the rotational position of the rotating drum.